The present invention relates to a process for dispersing hydroxypropyl methyl cellulose in a nonaqueous liquified organic medium in which it does not swell or dissolve, and subsequently adding said dispersion to an aqueous-containing liquid formulation wherein it is readily solubilized.
Hydroxypropyl methyl cellulose is often used as a thickening agent in aqueous-containing liquid formulations such as liquid detergents, shampoos, liquid hand soaps and the like. However, processing difficulties are encountered when dispersing and incorporating hydroxypropyl methyl cellulose into liquid formulations containing water, using conventional methods of dispersion. These known methods include dispersion in hot water at temperatures of 80.degree.-100.degree. C. (176.degree.-212.degree. F.); dispersion in water miscible organic solvents such as alcohol or glycol; and dispersion by dry blending with dry powders. The disadvantages of aforesaid conventional methods are the use of large amounts of energy in the form of heat and long mixing cycles; and the presence of flammable solvents such as alcohol which creates the danger of inflammability.
Still another difficulty encountered with aforesaid dispersion methods is the formation of lumps of undissolved hydroxypropyl methyl cellulose in the aqueous medium, which do not dissolve even after protracted periods of agitation (about 2-3 hours). This lumping problem requires an additional filtration step to rid the liquid formulation of said undissolved material. In addition, it is necessary to heat the water to high temperatures of about 75.degree.-100.degree. C. to effect dispersion of the hydroxypropyl methyl cellulose therein. This is shown in U.S. Pat. No. 3,953,591 wherein is disclosed the method of preparing a skin conditioning emulsion by separately heating the oil phase and the water phase containing the hydroxypropyl methyl cellulose, each to a temperature of 75.degree.-100.degree. C., and slowly adding the heated oil phase to the water phase with stirring (column 4 lines 21-34).
U.S. Pat. No. 3,549,542 also discloses the necessity of using hot water heated to a temperature of 180.degree.-200.degree. F. for dispersing the hydroxypropyl methyl cellulose in water prior to the addition of an aqueous solution of a cationic polymer to form a premix, which is subsequently dispersed in an aqueous solution of an anionic detergent, followed by milling in a colloid mill, to form a homogeneous liquid detergent composition.
U.S. Pat. No. 3,998,761 also discloses the necessity of using water heated to a temperature of about 185.degree.-190.degree. F. to slowly disperse hydroxypropyl methyl cellulose powder under rapid lightning agitation and the addition, with agitation, of a formaldehyde solution in the formation of a lump free mucilage. This mucilage is prepared a day prior to its addition to a shampoo formulation.
U.S. Pat. No. 4,174,305 discloses the preparation of a granular detergent composition by combining all the components except the cellulose ether (Methocel HB 15000) in an aqueous crutcher slurry, spray drying to granule form and adding the cellulose ether to the granules as a dry admix. The liquid compositions are prepared by mixing the components in a liquid carrier of water or water and alcohol.
However, there is no disclosure of the preparation of a premix of hydroxypropyl methyl cellulose dispersed in an aqueous-free liquified organic medium in which it does not swell or dissolve, selected from the group consisting of liquified nonionic surfactants, fatty acids, anionic surfactants and mixtures thereof, prior to its incorporation into an aqueous-containing liquid formulation, using a short mixing cycle.